A photocoupler (including a photorelay) can convert an input electric signal into an optical signal using a light emitting element, receive the optical signal using a light receiving element, and then output an electric signal. Hence, the photocoupler can transmit an electric signal in a state where the input side and the output side are insulated from each other.
In industrial equipment, office equipment, and household electrical equipment, different power supply systems such as a DC voltage system, an AC power supply system, a telephone line system, and a control system are arranged in one equipment. However, if different power supply systems are directly connected, an operational malfunction may occur.
If the photocoupler is used, insulation is provided between different power sources and therefore the operational malfunction can be suppressed.
For example, a large number of photocouplers, including those for AC loads, are used in inverter air conditioners etc. In the case of signal switching in LSI testers, a very large number of photocouplers are used. In such a case, downsizing is strongly required from the necessity to reduce the area of mounting onto a substrate. Even with a small size, it is required to maintain high moisture resistance and reliability.